In air brake systems, a drop-in air brake fitting is used in the lines leading from an air source, such as a wet tank, to either the primary or secondary air chambers of the brake system. To prevent loss of pressure in the primary and secondary air chambers, if there is a leak in the system, such as at the wet tank, a one-way check valve is usually assembled on the fitting. Currently, one-way check valves, which are designed and manufactured for truck air brakes are either machined out of brass or molded out of plastic to have a smooth, cylindrical bore and then a spring and valve member are assembled in the bore.